Method

Begin by making the pastry as described in shortcrust pastry, adding the cheddar cheese, mustard powder and cayenne to the rubbed in mixture before you add the water. Click here for shortcrust pastry.

Then leave it to rest in a polythene bag in the refrigerator for 30 minutes.

Meanwhile, you can be preparing the filling.

Melt the butter in a heavy-based saucepan, then add the chopped onions, stir to get them well coated in the butter, and cook them (uncovered) over a medium heat for about half an hour until they have reduced and turned a deep brown.

Give them a stir from time to time to prevent them catching on the bottom of the pan and, if at the end of the time they haven't turned almost mahogany brown, turn the heat up and cook for a further 10 minutes.

Roll the rested pastry out as described in the shortcrust pastry recipe to 28cm in diameter then carefully roll the pastry round the rolling pin and transfer it to the centre of the tin.

Now, using your hands, gently press the pastry into the tin to line the base and sides making sure you ease the pastry into the corners and press it against the sides then trim off any excess pastry around the top edge with a sharp knife.

After that use your fingers again to press the sides all round to the pastry so it is slightly proud of the tin.

All you now need to do is prick the base all over with a fork, as this will release any trapped air, which is what causes the centre to rise up. Then pop it in the freezer to chill for 30 minutes.

Pre-heat the oven to 190°C gas mark 5 with the baking sheet on the shelf nearest the centre.

Once the pastry case is frozen put it on a flat surface. Place the piece of foil over it, then press it down over the base and up the sides of the pastry. Turn the edge of foil inwards and crumple it against the sides to create a support that will hold the pastry in place whilst it cooks.

Put the pastry case onto the pre-heated tray in the oven and bake for 15 minutes. Then remove the pastry case from the oven and ease the sides of the foil inwards and carefully lift it away from the pastry case (you can reserve this foil liner to use another time).

Brush the base and sides all over with beaten egg (use a little from the filling), which will provide a sort of moisture proof coating so that the pastry stays beautifully crisp even after the filling has gone in. Now return the pastry case to the oven for 7-8 minutes.

Remove the cooked pastry case from the oven and reduce the oven temperature to 180°C, gas mark 4, then spread half of the onions all over the base of the tart then whisk the beaten eggs together with the cream and some seasoning

Pour half the egg mixture all over the onions then spoon over the remaining onions and pour in the remaining egg mixture (depending on how much the onions have reduced, there may be a tiny spot left over).

Finally sprinkle the cheese over the top.

Carefully slide the tart on its baking sheet back into the oven and bake for 35 – 40 minutes or until the filling is puffy and golden brown.

Leave to rest in the tin for at least 10 minutes then place the tart on an upturned bowl and gently slide the tin downwards. Then use a palette knife gently to slide the tart from the base onto a serving dish or cooling rack.

Note: This tart is also good made with Parmesan pastry and if you like you can add a tablespoon of finely chopped sage to the egg filling and arrange some sage leaves on the top before it is sprinkled with cheese and baked.